Watermark Crown CC reversed, perforation 12 1/2.
It could have been any of Perforated 1861-1890
Watermark 33 (swan) ,34 (crown over CC) or ,or 35 (Crown over CA)
Opinion: A drastic damage like your would have been widely known, I have not come across it in my time, but let's see........
I'll do some more research.
16th May 1864 PMG ordered 2,000 sheets of the 6d on Crown CC paper.
First despatch was fowarded on the steamer "Poonah" by De la Rue 19th September 1864
These printings were made by a line machine guage 12.5
(The old line 13 machine was used , having been re-aligned and cleaned, and generally overhauled...resulting in a 12.5 guage)